Email server with enhanced least recently used (LRU) cache

ABSTRACT

An electronic mail (email) server includes a proxy that obtains mappings for unique identifiers (UID&#39;s) corresponding to new electronic messages that have been determined from a polling operation. A Least Recently Used (LRU) cache caches each new message and releases from cache least recently used messages. A memory in which all messages within the LRU cache are spooled.

FIELD OF THE INVENTION

The present invention relates to the field of communications systems,and, more particularly, to electronic mail (email) communicationssystems and related methods.

BACKGROUND OF THE INVENTION

Electronic mail (email) has become an integral part of business andpersonal communications. As such, many users have multiple emailaccounts for work and home use. Moreover, with the increasedavailability of mobile cellular and wireless local area network (LAN)devices that can send and receive emails, many users wirelessly accessemails from mailboxes stored on different email storage servers (e.g.,corporate email storage server, Yahoo, Hotmail, AOL, etc.).

Yet, email distribution and synchronization across multiple mailboxesand over wireless networks can be quite challenging, particularly whenthis is done on a large scale for numerous users. For example, differentemail accounts may be configured differently and with non-uniform accesscriteria. Moreover, as emails are received at the wirelesscommunications device, copies of the emails may still be present in theoriginal mailboxes, which can make it difficult for users to keep theiremail organized.

One particularly advantageous “push” type email distribution andsynchronization system is disclosed in U.S. Pat. No. 6,779,019 toMousseau et al., which is assigned to the present Assignee and is herebyincorporated herein by reference. This system pushes user-selected dataitems from a host system to a user's mobile wireless communicationsdevice upon detecting the occurrence of one or more user-defined eventtriggers. The user may then move (or file) the data items to aparticular folder within a folder hierarchy stored in the mobilewireless communications device, or may execute some other systemoperation on a data item. Software operating at the device and the hostsystem then synchronizes the folder hierarchy of the device with afolder hierarchy of the host system, and any actions executed on thedata items at the device are then automatically replicated on the samedata items stored at the host system, thus eliminating the need for theuser to manually replicate actions at the host system that have beenexecuted at the mobile wireless communications device.

The foregoing system advantageously provides great convenience to usersof wireless email communication devices for organizing and managingtheir email messages. Yet, further convenience and efficiency featuresmay be desired in email distribution and synchronization systems asemail usage continues to grow in popularity.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is schematic block diagram of a direct access electronic mail(email) distribution and synchronization system in accordance with thepresent invention.

FIG. 2 is a schematic block diagram of an exemplary embodiment of userinterface components of the direct access proxy of the system of FIG. 1.

FIG. 3 is a schematic block diagram of an exemplary embodiment of theWeb client engine of the system of FIG. 1.

FIG. 4 is a schematic block diagram of an exemplary embodiment of themobile office platform engine machine for use in the system of FIG. 1.

FIG. 5 is a schematic block diagram of an exemplary embodiment of thedatabase module of the system of FIG. 1.

FIGS. 6A and 6B are high-level flowcharts illustrating operation of anelectronic mail (email) server that obtains mappings for mapping messageidentifiers.

FIG. 7 is a high-level flowchart illustrating a process for reducing UIDmappings in cache.

FIG. 8 is a high-level flowchart illustrating a basic process ofimproving a Least Recently Used (LRU) cache.

FIG. 9 is a schematic block diagram illustrating an exemplary mobilewireless communications device that can be used with the Direct Accesssystem shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime notation is used toindicate similar elements in alternative embodiments.

Generally speaking, the present application is directed to a directaccess electronic mail system, and more particularly, to an electronicmail (email) server. The email server may include a proxy that obtainsmappings for unique identifiers (UID's) corresponding to new electronicmessages that had been determined from a polling operation. A LeastRecently Used (LRU) cache caches each new message and releases fromcache least recently used messages. A memory is included in which allmessages within the LRU cache are spooled.

This memory could be formed as a disk memory having an input/outputthrough which new messages are input and output. The input/output variesin its requests per second based on the number of proxies per partition.The input/output also has fewer requests per second when a greaternumber of proxies per partition exists on the disk memory. The proxy isalso operative for filtering out received headers from a new message toaid in reducing the overall size of a new message.

A communications system, electronic mail (email) processing method, andcomputer-readable medium having computer-executable modules is setforth. The computer-readable medium can include a Least Recently Used(LRU) cache and memory, such as disk memory.

Referring initially to FIG. 1, a direct access (DA) email distributionand synchronization system 20 allows direct access to different mailsources, allowing messages to be transferred directly to a mobilewireless handheld device from a source mailbox. As a result, differentmail stores need not be used for integrated external source mailaccounts, and a permanent copy of an email in a local email store is notrequired.

Although this diagram depicts objects as functionally separate, suchdepiction is merely for illustrative purposes. It will be apparent tothose skilled in the art that the objects portrayed in this figure canbe arbitrarily combined or divided into separate software, firmware orhardware components. Furthermore, it will also be apparent to thoseskilled in the art that such objects, regardless of how they arecombined or divided, can execute on the same computing device or can bearbitrarily distributed among different computing devices connected byone or more networks.

The direct access system 20 enables email users or subscribers to haveemail from third party email services pushed to various mobile wirelesscommunications devices 25. Users need not create a handheld emailaccount to gain direct access to an existing external email account. Thedirect access system 20 may operate without performing aggregation asused in some prior art systems, in which emails are aggregated frommultiple different source mailboxes to a single target mailbox. In otherwords, email need not be stored in an intermediate target mailbox, butinstead may advantageously be accessed directly from a source mailstore.

As illustrated in FIG. 1, the direct access system 20 illustrativelyincludes a Web client (WC) engine 22 and a mobile office platform (MOP)24. These Web client engine 22 and mobile office platform 24 operatetogether to provide users with direct access to their email from mobilewireless communications devices 25 via one or more wirelesscommunications networks 27, for example. Both the Web client engine 22and the mobile office platform 24 may be located at the same location orat separate locations, and implemented in one or more servers. The webclient engine 22 illustratively includes a port agent 30 forcommunicating with the wireless communications devices 25 via thewireless communications network(s) 27, a worker 32, a supervisor 34, andan attachment server 36, which will be discussed further below. An alertserver 38 is shown in dashed lines, and in one preferred embodiment, isnot used, but could be part of the system in yet other embodiments.

The mobile office platform 24 illustratively includes a DA proxy 40, anda proxy application programming interface (API) 42 and a cache 44cooperating with the DA proxy. The mobile office platform 24 alsoillustratively includes a load balance and cache (LBAC) module 46, anevent server 48, a universal proxy (UP) Servlet 54, an AggCron module56, a mobile office platform (MOP) engine 58, and a database (DB) engine60, which will be discussed in further detail below. The Least RecentlyUsed (LRU) cache 41 caches new messages, and can release messages andobjects that were least recently used.

The supervisor 34 processes new mail notifications that it receives fromthe direct access proxy 40. It then assigns a job, in the form of a UserDatagram Protocol (UDP) packet, to the least-loaded worker 32, accordingto the most recent UDP heartbeat the supervisor 34 has received. Forpurposes of this description, heartbeat is a tool that monitors thestate of the server. Additionally, the supervisor 34 will receive a newservice book request from the direct access proxy 40 to send servicebooks to the mobile wireless communication device for new or changedaccounts. A service book can be a class that could contain all servicerecords currently defined. This class can be used to maintain acollection of information about the device, such as connectioninformation or services, such as an email address of the account.

The worker 32 is an intermediary processing agent between the supervisor34 and the port agent 30, and responsible for most processing in the Webclient engine 22. It will retrieve e-mail from a universal proxy 54, viaa direct access proxy, and format e-mail in Compressed MultipurposeInternet Mail Extension (CMIME) as a type of Multipurpose Internet MailExtension, and send it to the port agent 30, for further processing. Itsresponsibilities include the following tasks: (1) messages sent to andreceived from the handheld; (2) message reply, forward and morerequests; (3) Over The Air Folder Management operation (OTAFM); (4)attachment viewing; and (5) service book.

The port agent 30 acts as a transport layer between the infrastructureand the rest of the Web client engine 22. It is responsible fordelivering packets to and from the mobile wireless communicationsdevice. To support different integrated mailboxes with one device, morethan one service book can be used, and each service book can beassociated with one integrated mailbox. A port agent 30 can include oneServer Relay Protocol (SRP) connection to a relay, but it can alsohandle multiple SRP connections, and each connection may have a uniqueGlobally Unique Identifier (GUID) associated with a service book. Theattachment server 36 provides service for document/attachment conversionrequests from workers 32.

The direct access proxy 40 provides a Web-based Distributed Authoringand Versioning (WebDAV) interface that is used by the worker 32 toaccess account and mailbox information. This provides functionality tocreate, change and move documents on a remote server, e.g., a Webserver. The direct access proxy 40 typically will present anasynchronous interface to its clients. The LBAC module 46 is used by anotification server and the Web client engine 22 components to locatethe proper DA proxy for the handling of a request. The universal proxyServlet 54 abstracts access to disparate mail stores into a commonprotocol. The event server 48 responds to notifications of new messagesfrom corporate servers 52 and/or mail service providers 50, which may bereceived via the Internet 40, for example. The notifications arecommunicated to the direct access proxy 40 by the AggCron module 56 andthe event server 48 so that it may initiate checking for new mail onsource mailboxes 51, 53 of the mail service providers 50 and/orcorporate servers 52. The proxy API can be a Simple Object AccessProtocol (SOAP) Daemon 42 and is the primary interface into a database60, which is the primary data store for the mobile office platform 24.The AggCron module 56 may also periodically initiate polling for newmessages as well.

FIG. 2 is a high-level block diagram showing user interface componentsof the direct access proxy 40. More particularly, the direct accessproxy 40 illustratively includes an identifier module 72 with variousdownstream proxy modules for different communication formats, such as aWireless Application Protocol (WAP) proxy module 74 and a HypertextMarkup Language (HTML) proxy module 76. Of course, it will beappreciated by those skilled in the art that other types of proxymodules for other communications formats may also be used.

The identifier module 72 provides a centralized authentication servicefor the direct access system 20 and other services. An authenticationhandshake may be provided between an ID service and direct access system20 to ensure that users have the proper credentials before they areallowed access to the direct access system 20. The ability to switchfrom managing a Web client to a direct access system, or vice versa, mayoccur without requiring the user to re-enter any login credentials. AnyWeb client and direct access may share session management information onbehalf of a user.

The WAP proxy 74 provides a wireless markup language (WML)-based userinterface for configuring source mailboxes with the mobile officeplatform 24. The HTML proxy 76 provides an HTML-based user interface forconfiguring of source mailboxes in the MOP 24. The proxy API 42 (SOAPDaemon) is the primary interface into the database 60. The engine 58 isa protocol translator that connects to a source mailbox to validateconfiguration parameters. The database 60 is the primary user data storefor the mobile office platform 24.

FIGS. 3, 4 and 5 illustrate respective Web client engine machines 80(FIG. 3), an engine machine 82 (FIG. 4), and database machine 84 (FIG.5). The Web client engine machine 80 illustratively includes thesupervisors 34, workers 36, and port agents 38. Relays 86 cooperate withthe port agents 38 using a GUID.

The engine machine 82 illustratively includes a direct access proxy 40,HTML proxy 76, WAP proxy 74, PDS module 88, UP Servlet 54, LBAC module46, a sendmail module 90, an secure mail client (SMC) server 92, asecure sockets layer (SSL) proxy 94, an aggregation engine 96, and eventserver 48. The SMC server 92 cooperates with corresponding SMC modulesresident on certain corporate networks, for example, to convey emaildata between the mobile office platform 24 and source mailboxes. Thedatabase machine 84 may include an aggregation application programminginterface (API) 100 as a SOAP Daemon, an administration console 102, anaggregation database 104, the AggCron module 56, an SMC directory server106, and a send mail module 90.

The various components of the Web client engine 22 may be configured torun on different machines or servers. The component binaries andconfiguration files may either be placed in a directory on the networkor placed on a local disk that can be accessed to allow the appropriatecomponents to run from each machine. In accordance with one exemplaryimplementation, deployment may include one supervisor, two workers, andone port agent for supporting 30,000 external source mailboxes, althoughother configurations may also be used. Actual production deployment maydepend on the results of load, performance and stress testing, as willbe appreciated by those skilled in the art.

For the mobile office platform 24 direct access components, modules andvarious functions, machines are typically installed in twoconfigurations, namely engine machines (FIG. 4) and database machines(FIG. 5). While these machines may have all of the above-describedcomponents installed on them, not all of these components need be activein all applications (e.g., aggregation may be used with systems that donot support push technology, etc.). Once again, actual productiondeployment may depend on the results of load, performance and stresstesting.

The mobile office platform 24 architecture in one known techniqueadvantageously uses a set of device/language-specific extensibleStylesheet Language (XSL) files, which transform application data intopresentation information. In one non-limiting example, a build processtakes a non-localized XSL and generates a localized XSL for eachsupported language. When the XSL is used, it is “compiled” in memory andcached for repeated use. The purpose of pre-localizing and caching thetemplates is to reduce the CPU cycles required to generate apresentation page.

Branding may also be performed. Initially, a localized XSL may build aWAP application to access aggregated email accounts. A WAP proxyapplication may be localizable and support multiple WAP devices. Foreach logical page of an application, a device-specific XSL may becreated, which may be localized for each language/country supported.This rendering scheme may support not only WAP devices, but also SMTP,HTML and POP proxies, for example. In branding, each page of a givenapplication may be customized for each different brand.

The branding of a page may be accomplished through XSL imports,including the use of a Java application programming interface (API) forXML processing (JAXP) feature to resolve the imports dynamically. Thisneed not require that each combined page/brand template be compiled andcached. By way of example, in a sample template directory, first andsecond pages for a single language/country may be combined with brandedcounterparts to generate a plurality of distinct template combinations.It is also possible to profile memory requirements of an application byloading templates for a single language, device/application and brand.An HTML device may include a set of templates that are large compared toother devices.

In one known technique, the mobile office platform 24 advantageouslybuilds processes and takes non-localized files and language-specificproperty files and combines them to make each non-localized XSL into anXSL for each supported language. A separate XSL for each language neednot be used, and the language factor may be removed from the memoryusage equation. A JAXP API may be used to extend XSL with Java classes.The extensions may take various forms, for example, including extensionelements and extension functions. A template may be transformed bycreating and initializing an extension object with a locale and passingan object to a transformer. The system can remove multiple imports anduse less memory. HTML templates can use template importing to enabletemplate reuse, much like Java classes, and reuse other Java classesthrough a mechanism like derivation or importing.

In the direct access system 20, users receive email on their mobilewireless communications devices 25 from multiple external accounts, andwhen replying to a received message, the reply-to and sent-from addressintegrity is preserved. For example, for a user that has an integratedYahoo! account (user@yahoo.com) and a POP3 account (user@pop3.com), ifthey receive an email at user@yahoo.com, their replies generated fromthe device 25 will appear to come from user@yahoo.com. Similarly, if auser receives an email at user@pop3.com, their replies will appear tocome from user@pop3.com.

Selection of the “sent from” address is also available to a user thatcomposes new messages. The user will have the ability to select the“sent from” address when composing a new message. Depending on thesource mailbox type and protocol, the message may also be sent throughthe source mail service. This functionality can be supported by sendinga configuration for each source mailbox, for example, as a non-limitingexample, a service book for each source mailbox 51, 53 to the mobilewireless communications device 25.

As noted above, a service book is a class that may include all servicerecords currently defined. This class may be used to maintain acollection of information about the device, such as connectioninformation. The service book may be used to manage HTTP connections andmail (CMIME) information such as account and hierarchy. At mobilewireless communications devices 25, a delete service book request may besent when a source mailbox 51, 53 is removed from the account. Theservice book may also be resent to the device 25 with a viewable namethat gives the user some indication that the selection is no longervalid.

A sent items folder may also be “synchronized.” Any device-originatedsent messages may be propagated to a source account and stored in a sentmail folder, for example. Also, messages deleted on the device 25 maycorrespondingly be deleted from the source mailbox 51, 53. Anotherexample is that device-originated marking of a message as read or unreadon the device 25 may similarly be propagated to the source mailbox 51,53. While the foregoing features are described as source-dependent andsynchronizing one-way, in some embodiments certain synchronizationfeatures may in addition, or instead, propagate from the sourcemailbox/account to the handheld device, as will be appreciated by thoseskilled in the art.

When available, the mail service provider or corporate mail server maybe used for submission of outgoing messages. While this may not bepossible for all mail service providers or servers, it is preferrablyused when available as it may provide several advantages. For example,subscribers to AOL will get the benefit of AOL-specific features likeparental controls. Furthermore, AOL and Yahoo users, as non-limitingexamples, will see messages in their sent items folder, and messagesrouted in this manner may be more compliant with new spam policies suchas Sender Policy Framework (SPF) and Sender Id. In addition, messagessent via corporate mail servers 52 will have proper name resolution bothat the global address list level and the personal level. It should beunderstood, however, that the use of the mail service provider 50 todeliver mail may be dependant on partner agreements and/or protocol,depending upon the given implementation.

The architecture described above also advantageously allows for featuressuch as on-demand retrieval of message bodies and attachments andmultiple folder support. Morever, a “this-is-spam” button or indicatormay be used allowing company labels and other service provider-specificfeatures when supported by an underlying protocol, as will beappreciated by those skilled in the art.

One particular advantage of the direct access system 20 is that a userneed not configure an account before integrating additional accounts.However, a standalone email address may be used, and this addressadvantageously need not be tied to a mailbox size which the subscriberis required to manage. For example, the email account may be managed byan administrator, and any mail could be purged from the system after apre-determined period of time (i.e., time-based auto-aging with nomailbox limit for all users).

Additionally, all aspects of any integrated email account creation,settings and options may advantageously be available to the user fromtheir mobile wireless communications device 25 Thus, users need notvisit an HTML site and change a setting, create a filter, or performsimilar functions, for example. Of course, an HTML site may optionallybe used.

As a system Internet email service with the direct access system 20grows, ongoing emphasis may advantageously be placed on theadministrative site to provide additional information to carrieradministrators, support teams, and similar functions. However, in someinstances a mail connector may be installed on a personal computer, andthis functionality may not always be available from the mobile wirelesscommunications device.

The Web client engine 22 may advantageously support different featuresincluding message to handheld (MTH), message from handheld (MFH),forward/reply a message, request to view more for a large message (e.g.,larger than 2K), request viewing message attachment, and over the airfolder management (OTAFM). These functions are explained below.

For an MTH function, each email account integrated for a user is linkedwith the user device through a Web client service book. For each newmessage that arrives in the Web client user mailbox, a notification thatcontains the new message information will typically be sent to a Webclient engine supervisor component (FIG. 3), which in turn will assignthe job to an available worker with the least load in the system. Thechosen worker 32 will validate the user information and retrieve the newmessage from the user source mailbox and deliver it to the user device.

In an MFH function, MFH messages associated with a Web client servicebook are processed by the Web client engine 22 and delivered to theInternet 49 by the worker 32 via the simple mail transfer protocol(SMTP) or native outbox. If a user turns on the option to save the sentmessage to the sent items folder, the direct access proxy will save acopy of the sent message to this folder.

In a Forward/Reply/More function, the user can forward or reply an MTHor MFH message from the mobile wireless communications device 25 as longas the original message still existed in the direct access proxy cacheor in user mailbox. For MTH, the worker 32 may send the first 2K, forexample, or the whole message (whatever is less) to the user device. Ifthe message is larger than 2K, the user can request MORE to view thenext 2K of the message. In this case, the worker 32 will process theMore request by retrieving the original message from the user sourcemailbox, and send back the 2K that the device requests. Of course, insome embodiments more than 2K of message text (or the entire message)may be sent.

In an attachment-viewing function, a user can view a message attachmentof a popular document format (e.g., MS Word, MS Power Point, MS Excel,Word Perfect, PDF, text, etc.) or image format (GIF, JPEG, etc). Uponreceiving the attachment-viewing request, which is implemented in a formof the More request in this example, the worker 32 can fetch theoriginal message from the user source mailbox via the direct accessproxy, extract the requested attachment, process it and send result backto the user device. The processing requires that the original messagehas not been deleted from the user Web client mailbox.

In the save sent message to sent items folder function, if the userturns this option on, the worker 32 places a copy of each MFH messagesent from the user device in the user sent items folder in the mailbox.In over the air folder management, the Web client OTAFM servicemaintains any messages and folders in the user mailbox synchronized withthe user device over the air.

Whenever a message in the user source mailbox is Moved/Deleted, theassociated message on the device may also be Moved/Deleted accordingly,and vice-versa. When a message is Moved/Deleted on the device, theassociated message in the user Web client mailbox may also beMoved/Deleted accordingly. Similarly, when a folder isAdded/Removed/Renamed from the user Web client mailbox, the associatedfolder on the device may be Added/Removed/Renamed, and vice-versa.

The system 20 may advantageously support different subsets of variousmessaging features. For example, in the message to handheld function,the mobile office platform 24 may be responsible for connecting to thevarious source mailboxes 51, 53 to detect new emails. For each new mail,a notification is sent to the Web client engine 22 and, based on thisnotification, the supervisor 34 chooses one of the workers 32 to processthat email. The chosen worker will fetch additional account informationand the contents of the mail message from the direct access proxy 40 anddeliver it to the user device 25.

In a message sent from handheld function, the MFH could be given to thedirect access proxy 40 from the Web client worker 32. In turn, themobile office platform 24 delivers a message to the Internet 49 bysending through a native outbox or sending it via SMTP. It should beunderstood, however, that the native outbox, whenever possible, mayprovide a better user experience, especially when taking into accountcurrent anti-spam initiatives such as SPF and sender Id.

In a message deleted from handheld function, when a message is deletedfrom the device 25, the Web client engine 22 notifies the mobile officeplatform 24 via the direct access proxy 40. As such, the mobile officeplatform 24 can delete the same message on the source mailbox.

When handling More/Forward/Reply/Attachment viewing requests, the Webclient worker 32 may request an original mail from the direct accessproxy 40. It will then process the request and send the results to themobile wireless communications device 25. The architecture mayadditionally support on-demand retrieval of message parts and otherupgrades, for example.

Upon the integration of a new source mailbox 51, 53, the service booknotification from the alert server 38 may be sent to the supervisor 34,which assigns this notification to a worker 32 for sending out a servicerecord to the device. Each source mailbox 51, 53 may be associated witha unique service record. In this way, each MFH message is linked with asource mailbox 51, 53 based on the service record on the device.

The system 20 may also poll the integrated external mailboxesperiodically to check for new mail and to access any messages. Thesystem 20 may further incorporate optimizations for polling bandwidthfrom an aggregation component allowing a quick poll. The system 20 canalso advantageously support a large active user base and incorporate arapidly growing user base.

The topology of load balancing can be based on the size of a component'squeue and its throughput. These load statistics can be monitored by amechanism in one example called the UDP Heartbeat, as described before.If a component is overloaded or has a large queue size, the componentwill have less chance to get an assigned job from other components. Incontrast, a component will get more assigned jobs if it completes morejobs in the last few hours than other components. With this mechanism,the load could distribute over heterogeneous machine hardware, i.e.,components running on less power machines will be assigned fewer jobsthan those on machines with more power hardware.

General load balancing for any mobile office platform components can beaccomplished through the use of a load balancer module, for example, aBIG-IP module produced by F5 Networks of Seattle, Wash. BIG-IP canprovide load balancing and intelligent layer 7 switching, and can handletraffic routing from the Internet to any customer interfacing componentssuch as the WAP and HTML proxies. The use of a BIG-IP or similar modulemay provide the application with pooling capabilities, fault toleranceand session management, as will be appreciated by those skilled in theart.

Typically, access to a single source mailbox 51, 53 can be from a singledirect access proxy 40 over a persistent connection. Any requests onbehalf of a particular user could persist to the same machine in thesame direct access clustered partition. As certain components aresystem-wide and will be handling work for users across many partitions,these components can be designed to determine which direct accesspartition to communicate with on a request-by-request basis.

The load balancer and cache (LBAC) 46 may support this function. TheLBAC 46 is a system-wide component that can perform two importantfunctions. The first of these function is that it provides a mappingfrom the device PIN to a particular direct access proxy 40, whilecaching the information in memory for both fast access and to save loadon the central database. Secondly, as the direct access proxy 40 will berun in clustered partitions, the LBAC 46 may distribute the load acrossall direct access proxies within any partition.

The LBAC 46 can be formed of different components. For example, the codewhich performs the load balancing can be an extended version of a securemail connector. The code can also perform lookups to the centraldatabase and cache the results (LBAC).

In one non-limiting example, when a worker requires that a direct accessproxy 40 perform work, it provides the LBAC 46 with a device PIN. TheLBAC 46 will discover which partition that PIN is associated with bylooking in its cache, or retrieving the partition identifier from acentral database (and caching the result). Once the partition is known,the LBAC 46 then consults its cache to see which direct access proxy inthat partition has been designated to handle requests for that PIN. Ifno mapping exists, the LBAC requests the PDS to create a new associationon the least loaded DA proxy 40 (again caching the result). Finally, theLBAC 46 responds to the worker 32 with the connection information forthe proper direct access proxy to handle that particular request.

The secure mail connector 88 may run in failover pairs, where one is anactive master and the other is a secondary standby. Internal datastructures may be replicated in real-time from the master to thestandby. Multiple LBACs 46 can be run for scalability and faulttolerance, but typically would require an external connection balancingcomponent, such as the BIG-IP component as explained before.

A receiving component in the Web client engine 22 saves the job that hasbeen assigned to it from other components to a job store on the diskbefore processing. It can update the status of the job and remove thejob from the job store when the job processing is completed. In case ofcomponent failure or if the process is restarted, it can recover thejobs from the job store and, based on the current statuses of thesejobs, continue processing these jobs to the next state, saving the timeto reprocess them from the beginning.

Any recovery from the standpoint of MTH/MFH can be achieved throughcurrent polling behavior and on the Web client engine 22 recoverymechanisms. From within the mail office platform components, until amessage has been successfully delivered to a Web client engine 22, thatmessage is not recorded in the partition database 60. During the nextpolling interval, the system can again “discover” the message andattempt to notify the Web client engine 22. For new mail events, if anevent is lost, the system can pick up that message upon receiving thenext event or during the next polling interval. For sources supportingnotifications, this interval could be set at six hours, as onenon-limiting example. For messages sent from the Web client engine 22,and for messages that have been accepted by the Web client engine,recovery can be handled by different Web client engine components.

The Web client engine 22 may advantageously be horizontally andvertically scalable. Multiple supervisors 34 can beregistered/configured with direct access proxies 40 to provide thedistribution of the notification load and the availability of engineservice. Multiple workers 32 and port agents 30 can run on the samemachine or across multiple machines to distribute load and achieveredundancy. As the number of users grows, new components can be added tothe system to achieve high horizontal scalability.

It is possible for a new component to be added/removed to/from thesystem automatically without down time. Traffic can automatically bedelegated to a new component and diverted away from failed components.Each component within the mobile office platform 24 can be deployedmultiple times to achieve horizontal scalability. To achieve verticalscalability, each mobile office platform 24 component can be amulti-threaded process with a configurable number of threads to scaleunder heavy load. Pools of connections can be used to reduce theoverhead of maintaining too many open connections.

Currently, every time the DA proxy 10 receives a “check for new mail”notification, it obtains all the message identifiers, uniqueidentifiers, and Href attributes as a “path” or “handle” to a message(msgId, uid, and href) mappings from the database 60 and caches them. Inthis description, HREF is a mechanism used to identify and retrieve aparticular message from a source mailbox. It typically has meaning to aUP Servlet. Similarly, in case the DA proxy 10 receives aGet/Delete/Move request for a MsgId and it does not find it in the cache44, it accesses the database and obtains all the msgId, uid, and hrefmappings and caches them. Once cached, these mappings will reside forthe life of the user session. The database 60 can include a disk memoryin which messages or portions of messages can be spooled. A disk memoryto which messages or portions of messages can be spooled could beseparate from the database physical structure, of course.

The Href attribute is operative to retrieve a destination universalresource locator (URL), e.g., anchor point can jump to the bookmarks ofany other object identification attributes. A link could possiblydisplay any directory containing a current page, or could generate anerror depending on other elements on the web page and the serverenvironment. When an anchor is specified, the link to that address isrepresented by the text between opening and closing anchor tags. TheHref could also be considered a uniform resource locator being linked,making the anchor into a link. The message identifiers can be uniqueidentifiers (UID) as are known to those skilled in the art. The Href,msgID and UID terms can be called by different names as known by thoseskilled in the art.

It should be understood that some mailboxes have 1000+messages andothers have up to 10,000+messages in an Inbox and there could also becertain optimizations. In the database, (msgId, davUid, davHref) aredeclared as (int, varbinary (64), varbinary (255), typically about amaximum of 327 bytes per mapping. DAV can refer to distributed authoringand versioning, and in one implementation, data sizes and names couldchange.

In one optimization example, instead of fetching all the msgId mappings,the system could retrieve a smaller number, for example, the latest 100,when the system is about to perform a quick poll. The system does notrequire a full reconcile, and it is able to retrieve all UID's only whenthe system is about to make a full poll. If the system observes aGet/Delete/Move request on a msgId that is not cached, the system couldadd another stored procedure call that gives it the mapping for thisparticular msgId and, as an example, another 100 mappings around it.

Sample data suggests that the average mailbox size on a Work Clientproduction is 200. A typical mailbox, however, has 2000 UID's. Each DAproxy partition typically can support at least about 30,000 mailboxes.If the system deploys three proxies per partition, then each proxy cansupport about 10,000 mailboxes in this non-limiting example.

As an example, the average mailbox size is typically about 200. Theaverage UID mapping will occupy 200 bytes (60% of 327). Hence, eachmailbox will require (200*200=) 40 KB, and each proxy will require (40KB*10,000=) 400 MB to store these mappings. If 30% of all users will beactive at any given time, the memory requirement reduces to 30% of 400MB=120 MB. Similarly, if the system uses four proxies per partition,then the total memory requirement comes down to about 30% of (40KB*7,500)=90 MB in this example.

In one embodiment, three out of four polls in the DA system 10 are quickpolls. If the system introduces this optimization, it does not have tocache all the UID mappings 75% of the time, and thus, the system cansignificantly reduce the total memory requirement to cache thesemappings.

The main issue with fetching a subset, for example, 100, of all UID's inorder to check for new mail is that it can give the system falsepositives. If a UID from a remote server is a new, or is a visible UIDby checking for existence in the list of seen UID's, the system couldobtain a false positive, since we will be checking against a subset ofseen UID's and not the entire set of seen UID's. False positives willresult in duplicate mails being delivered to the device as new mail.

One way of getting around this problem is to fetch all the UID's fromthe database if the system comes across a new mail while doing a quickpoll in order to make sure it is a new UID. This approach couldintroduce an additional database hit every time a new mail isdiscovered. The extra database hit would not be necessary if a quickpoll does not discover any new mail.

Another optimization can be introduced in case the DA proxy 10 receivesa Get/Delete/Move request for a msgId and it does not find that in thecache. In this case, the system will fetch and cache all mappingsirrespective of the poll type, quick or full. This approach does notaffect the total memory requirement to cache these mappings duringpolling but will provide some benefit if a session does not see anypolling requests during its life, in which case it would not fetch allthe mappings and cache them but cache only a subset.

A different approach would be to fetch all the UID mappings from thedatabase and store them in a file-based cache instead of in memory. Thiswould not only address the concern the system has about memory consumed,but also eliminate the need for an extra database hit. On the otherhand, this type of system is much more complex to implement as opposedto storing the mappings in memory. It also could possibly decrease theperformance since the list has to be accessed from disk.

Another possible approach makes a stored procedure (proc) call with abatch of UID's in the right order, and implements the quick poll logicin the stored proc call. This approach is available since the quick polllogic is rather straightforward, and it would eliminate a requirement toread all the UID mappings into memory. The quick poll logic, however,requires the system to look at the top and the bottom of the mailbox tocheck for new mail, in which case it would result in two separate hitsto the database, once with the batch of UID's from the top, and a secondtime with the UID's from the bottom of the mailbox.

One method to reduce the memory requirement would be to purge the UID'sthat have been read into memory after the polling step is over. Once thequick or full poll is done, the system can proactively remove the UID'sthat have been read into memory. This polling logic requires only theUID's, and it does not require the msgId or the davHref. These are nolonger read from the database into memory. The new UID mappings thathave been discovered in the polling step are cached into memory, inorder to avoid a database hit when the worker asks for them.

If a Get/Delete/Move request is evident on a msgId that is not cached,another stored procedure call gives the system the mapping for thisparticular msgId, and 20 other mappings around it are added. Thesemappings are subsequently cached in memory. When the system asks thedatabase to return the mappings for a particular msgId, the systemretrieves mappings for 20 other msgIds around it, assuming that the usermight operate on other messages around the one that the user iscurrently operating on. Checks are placed to make sure that the numberof cached mappings do not keep growing and the cache is cleared if thenumber exceeds a certain threshold. The memory consumed by each usersession to cache the UID mappings is greatly reduced.

In the DA proxy architecture 40, there is a LRU cache 41 that caches allnew messages that it finds. Each DA proxy partition could see up to onemillion new messages a day, for example, 30,000 users each receiving 30messages a day, and the memory requirements of this data structure arelarge. For example, if the system decides to cache 1K of each message inmemory and spool anything over 1K to disk, and assuming every message isat least 1K in size, the cache would require one gigabyte of memory. Inorder to improve upon this, one possible approach is to add aweight/value to each message based on a heuristic, e.g., its messagesize or the number of times it would be accessed. Every time a messageis accessed, its associated value could be decremented. When this valueturns zero, the system would proactively delete this message item fromthe cache, instead of waiting for the LRU to operate. The total memoryconsumption of this data structure could be reduced.

This approach relies on knowledge of the internal workings of thesystem. For example, messages less than 3K in size are pushed in theirentirety to the device, and are likely to be accessed only twice, i.e.,once the first time it is pushed to the device, and the second time ifthe user decides to reply or forward the message. Messages greater than3K in size can be accessed once for every “More” request by the user,indicating that the user desires to view additional portions of themessage. Messages with attachments, however, may follow a differentpattern of requests unique to the working of the attachment server.

If the resulting heuristic is narrow, the system may end up deleting amessage from the cache prematurely, and thus, have to download themessage a second time. This could possibly increase bandwidth usage. Onthe other hand, if the heuristic is wide, the system may not deletemessages until the LRU forces them out, thus failing to derive anybenefit from the optimization.

Instead of keeping a certain portion of a message, for example, up to1K, in memory and spooling the rest onto disk, it is also possible thatmessages can be retained entirely in memory or entirely on disk. Sincethese are new messages that the worker is going to retrieve in theirentirety, keeping some portion in memory does not aid the overallresponse time of this request if the remaining portion will require adisk read.

One example data sample from the Work Client production finds thedistribution of message sizes. The data indicated that 37% of allmessages were less than 3K in size. One approach would be to keepmessages less than 3K entirely in memory, and messages greater than 3Kentirely on disk. In this case, the memory requirements would still beconsiderably high, 3K* 370K(37% of 1 M messages)=1.1 G.

This example data also indicated that typically 2% of all messages areabout less than 1K. Since the percentage of these messages is small,storing only messages less than 1K entirely in memory would notsignificantly affect the overall performance. In one embodiment, then,messages in cache can be spooled entirely on disk. This not only reducesthe main memory requirements of the cache to zero, but not having anyheuristic and relying on plain LRU reduces the likelihood of deletingmessages prematurely and then having to download them a second time,increasing bandwidth usage.

An example DA system request rate performance spreadsheet indicates thefollowing requirements that the DA proxy 40 (per partition) can support.Those requests that involve reading or writing to the message cache inthis example are:

New mail 621,000 msg/day Reply/Forward 124,000 msg/day More  31,000msg/day Total 776,000 msg/day

776,000 requests over a 12 hour period amounts to about 18 requests/sec.It is possible to use multiple proxies. If the system uses one DA proxy40 per partition, as long as the disk I/O can give the system 18requests per second, the system should be operable in its intendedmanner. If the system uses two DA proxies 40 per partition, then thesystem may require about 9 requests/second.

It is also possible to filter out the “Received” headers from thedownloaded messages and reduce the overall size of the message, andhence the memory consumed by each message in the cache.

FIGS. 6A, 6B, 7 and 8 are high-level flowcharts illustrating examples ofthe processes for obtaining mappings for new UID's and mapping newmessage ID's (FIG. 6), reducing UID mappings in cache (FIG. 7), andimproving the LRU cache (FIG. 8).

FIG. 6A shows that a polling function can start (block 200). The UID'sand message ID's of new mail are stored in a persistent store such as adatabase (block 202). The message ID's of new mail are cached to a cachememory (block 204) and the polling is complete. As shown in FIG. 6B, amail job is received (block 210) and a determination is made if amessage ID is in cache (block 212). If so, a mapping is obtained fromcache (block 214) and the mail job processed (block 216). The mail jobis complete (block 218). Alternatively, the message ID and adjacentmessage ID's can be retrieved from the persistent store as a data store(block 220) and the message ID is cached in the cache memory (block222).

As shown in FIG. 7 in this function, the polling can start (block 230).All previously existing UID's can be fetched and cached from thepersistent store as a database (block 232). The UID's and message ID'sfor new mail can be stored in the persistent store (block 234). Themessage ID's for new mail can be stored in a message ID cache (block236). All previously existing UID's can be cleared from the cache (block238) and the polling is complete (block 240).

As shown in FIG. 8, the polling can start (block 250). The UID's andmessage ID's of new mail can be stored in a persistent store as adatabase (block 252). The message ID's or new mail can be cached to acache memory (block 254). Each message can be retrieved and added intothe LRU (block 256). The messages can be spooled to a disk (block 258).The polling is complete (block 260).

An example of a hand-held mobile wireless communications device 1000that may be used is further described in the example below withreference to FIG. 9. The device 1000 illustratively includes a housing1200, a keypad 1400 and an output device 1600. The output device shownis a display 1600, which is preferably a full graphic LCD. Other typesof output devices may alternatively be utilized. A processing device1800 is contained within the housing 1200 and is coupled between thekeypad 1400 and the display 1600. The processing device 1800 controlsthe operation of the display 1600, as well as the overall operation ofthe mobile device 1000, in response to actuation of keys on the keypad1400 by the user.

The housing 1200 may be elongated vertically, or may take on other sizesand shapes (including clamshell housing structures). The keypad mayinclude a mode selection key, or other hardware or software forswitching between text entry and telephony entry.

In addition to the processing device 1800, other parts of the mobiledevice 1000 are shown schematically in FIG. 9. These include acommunications subsystem 1001; a short-range communications subsystem1020; the keypad 1400 and the display 1600, along with otherinput/output devices 1060, 1080, 1100 and 1120; as well as memorydevices 1160, 1180 and various other device subsystems 1201. The mobiledevice 1000 is preferably a two-way RF communications device havingvoice and data communications capabilities. In addition, the mobiledevice 1000 preferably has the capability to communicate with othercomputer systems via the Internet.

Operating system software executed by the processing device 1800 ispreferably stored in a persistent store, such as the flash memory 1160,but may be stored in other types of memory devices, such as a read onlymemory (ROM) or similar storage element. In addition, system software,specific device applications, or parts thereof, may be temporarilyloaded into a volatile store, such as the random access memory (RAM)1180. Communications signals received by the mobile device may also bestored in the RAM 1180.

The processing device 1800, in addition to its operating systemfunctions, enables execution of software applications 1300A-1300N on thedevice 1000. A predetermined set of applications that control basicdevice operations, such as data and voice communications 1300A and1300B, may be installed on the device 1000 during manufacture. Inaddition, a personal information manager (PIM) application may beinstalled during manufacture. The PIM is preferably capable oforganizing and managing data items, such as e-mail, calendar events,voice mails, appointments, and task items. The PIM application is alsopreferably capable of sending and receiving data items via a wirelessnetwork 1401. Preferably, the PIM data items are seamlessly integrated,synchronized and updated via the wireless network 1401 with the deviceuser's corresponding data items stored or associated with a hostcomputer system.

Communication functions, including data and voice communications, areperformed through the communications subsystem 1001, and possiblythrough the short-range communications subsystem. The communicationssubsystem 1001 includes a receiver 1500, a transmitter 1520, and one ormore antennas 1540 and 1560. In addition, the communications subsystem1001 also includes a processing module, such as a digital signalprocessor (DSP) 1580, and local oscillators (LOs) 1601. The specificdesign and implementation of the communications subsystem 1001 isdependent upon the communications network in which the mobile device1000 is intended to operate. For example, a mobile device 1000 mayinclude a communications subsystem 1001 designed to operate with theMobitexm™, Data TACT™ or General Packet Radio Service (GPRS) mobile datacommunications networks, and also designed to operate with any of avariety of voice communications networks, such as AMPS, TDMA, CDMA, PCS,GSM, etc. Other types of data and voice networks, both separate andintegrated, may also be utilized with the mobile device 1000.

Network access requirements vary depending upon the type ofcommunication system. For example, in the Mobitex and DataTAC networks,mobile devices are registered on the network using a unique personalidentification number or PIN associated with each device. In GPRSnetworks, however, network access is associated with a subscriber oruser of a device. A GPRS device therefore requires a subscriber identitymodule, commonly referred to as a SIM card, in order to operate on aGPRS network.

When required network registration or activation procedures have beencompleted, the mobile device 1000 may send and receive communicationssignals over the communication network 1401. Signals received from thecommunications network 1401 by the antenna 1540 are routed to thereceiver 1500, which provides for signal amplification, frequency downconversion, filtering, channel selection, etc., and may also provideanalog to digital conversion. Analog-to-digital conversion of thereceived signal allows the DSP 1580 to perform more complexcommunications functions, such as demodulation and decoding. In asimilar manner, signals to be transmitted to the network 1401 areprocessed (e.g. modulated and encoded) by the DSP 1580 and are thenprovided to the transmitter 1520 for digital to analog conversion,frequency up conversion, filtering, amplification and transmission tothe communication network 1401 (or networks) via the antenna 1560.

In addition to processing communications signals, the DSP 1580 providesfor control of the receiver 1500 and the transmitter 1520. For example,gains applied to communications signals in the receiver 1500 andtransmitter 1520 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 1580.

In a data communications mode, a received signal, such as a text messageor web page download, is processed by the communications subsystem 1001and is input to the processing device 1800. The received signal is thenfurther processed by the processing device 1800 for an output to thedisplay 1600, or alternatively to some other auxiliary I/O device 1060.A device user may also compose data items, such as e-mail messages,using the keypad 1400 and/or some other auxiliary I/O device 1060, suchas a touchpad, a rocker switch, a thumb-wheel, or some other type ofinput device. The composed data items may then be transmitted over thecommunications network 1401 via the communications subsystem 1001.

In a voice communications mode, overall operation of the device issubstantially similar to the data communications mode, except thatreceived signals are output to a speaker 1100, and signals fortransmission are generated by a microphone 1120. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the device 1000. In addition, the display 1600may also be utilized in voice communications mode, for example todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem enables communication betweenthe mobile device 1000 and other proximate systems or devices, whichneed not necessarily be similar devices. For example, the short-rangecommunications subsystem may include an infrared device and associatedcircuits and components, or a Bluetooth™ communications module toprovide for communication with similarly-enabled systems and devices.

This application is related to copending patent applications entitled,“EMAIL SERVER WITH PROXY CACHING OF UNIQUE IDENTIFIERS” and “EMAILSERVER WITH PROXY CACHING OF MESSAGE IDENTIFIERS AND RELATED METHODS,”which are filed on the same date and by the same assignee and inventors.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. An electronic mail (email) server comprising: a proxy that obtainsmappings for message identifiers (MsgID's) corresponding to newelectronic messages that had been determined from a polling operation; aleast recently used (LRU) cache that caches the MsgID's and apredetermined size of each new electronic message corresponding to theMsgID's and releases from the LRU cache the least recently used MsgIDand predetermined size of the new electronic message corresponding tothe MsgID; and a memory in which all messages within the LRU cache aresaved; the proxy receives a mail job, determines if a MsgID for the mailjob is in the cache, and if yes, obtains a mapping for the MsgID fromthe cache and processes the mail job, if the MsgID for the mail job isnot in the cache, retrieves the MsgID from a database, caches theretrieved MsgID into the cache, obtains a mapping for the retrievedMsgID from the cache and processes the mail job, and purges withoutusing weights and heuristics the cache of the MsgID's.
 2. The emailserver according to claim 1, wherein said memory comprises a disk memoryhaving an input/output through which the new electronic messages areinput and output.
 3. The email server according to claim 2, wherein saidinput/output varies in its request per second based on the number ofsaid proxies per partition.
 4. The email server according to claim 3,wherein said input/output has fewer requests per second when a greaternumber of said proxies per partition exist on the disk memory.
 5. Theemail server according to claim 1, wherein said proxy is operative forfiltering out received headers from a new electronic message to aid inreducing an overall size of a new electronic message.
 6. An electronicmail (email) server comprising: a least recently used (LRU) cache thatcaches the MsgID's and a predetermined size of each new electronicmessage corresponding to the MsgID's as determined from a pollingoperation and releases from the LRU cache the least recently used MsgIDand predetermined size of the new electronic message corresponding tothe MsgID; a disk memory in which all new electronic messages within theLRU cache are saved; and a proxy that receives a mail job, determines ifa MsgID for the mail job is in the cache, and if yes, obtains a mappingfor the MsgID from the cache and processes the mail job, if the MsgIDfor the mail job is not in the cache, retrieves the MsgID from adatabase, caches the retrieved MsgID into the cache, obtains a mappingfor the retrieved MsgID from the cache and processes the mail job, andpurges without using weights and heuristics the cache of the MsgID's. 7.The email server according to claim 6, wherein said disk memory includesan input/output through which the new messages are input and output. 8.The email server according to claim 7, wherein said input/output variesin its request per second based on the number of said proxies perpartition.
 9. The email server according to claim 8, wherein saidinput/output has fewer request per second when a greater number of saidproxies per partition exist on the disk memory.
 10. A communicationsystem comprising: a polling engine that polls an electronic mailbox ofa user to retrieve message identifiers (MsgID's) of new messages; aproxy that obtains mappings for the new message; a least recently used(LRU) cache that caches the MsgID's and a predetermined size of each ofthe new messages corresponding to the MsgID's and releases from the LRUcache the least recently used MsgID and predetermined size of the newmessage corresponding to the MsgID; and a memory in which all newmessages within the LRU cache are saved; the proxy receives a mail job,determines if a MsgID for the mail job is in the cache, and if yes,obtains a mapping for the MsgID from the cache and processes the mailjob, if the MsgID for the mail job is not in the cache, retrieves theMsgID from a database, caches the retrieved MsgID into the cache,obtains a mapping for the retrieved MsgID from the cache and processesthe mail job, and purges without using weights and heuristics the cacheof the MsgID's.
 11. The communications system according to claim 10,wherein said memory comprises a disk memory having an input/outputthrough which the new messages are input and output.
 12. Thecommunications system according to claim 11, wherein said input/outputvaries in its request per second based on the number of said proxies perpartition.
 13. The communications system according to claim 12, whereinsaid input/output has fewer request per second when a greater number ofsaid proxies per partition exist on the disk memory.
 14. Thecommunications system according to claim 12, wherein said proxy isoperative for filtering out received headers from a new message to aidin reducing an overall size of a new message.
 15. An electronic mail(email) processing method, which comprises: polling an electronicmailbox of a user to retrieve message identifiers (MsgID's) of newmessages; obtaining mappings for the new messages; caching the MsgID'sand a predetermined size of each new message corresponding to theMsgID's within a least recently used (LRU) cache; releasing the leastrecently used MsgID and predetermined size of the new messagecorresponding to the MsgID from the LRU cache; saving all messageswithin the LRU cache to memory; and receiving a mail job within a proxyand determining if a MsgID for the mail job is in the cache, and if yes,obtaining a mapping for the MsgID from the cache and processing the mailjob, and if the MsgID for the mail job is not in the cache, retrievingthe MsgID from a database, caching the retrieved MsgID into the cache,obtaining a mapping for the retrieved MsgID from the cache andprocessing the mail job, and purging without using weights andheuristics the cache of the MsgID's.
 16. A method according to claim 15,which further comprises spooling all new messages to a disk memory. 17.A method according to claim 16, which further comprises varying therequests per second in and out of the disk memory based on a proxy perpartition.
 18. A method according to claim 15, which further comprisesfiltering out received headers from a new message to aid in reducing anoverall size of new message.
 19. A computer-readable medium havingcomputer-executable modules comprising: a least recently used (LRU)cache that caches the MsgID's and a predetermined size of each of thenew electronic messages corresponding to the MsgID's as determined froma polling operation and releases from the LRU cache the least recentlyused MsgID and predetermined size of the new electronic messagecorresponding to the MsgID; a memory in which all messages within theLRU cache are saved; and a proxy that receives a mail job, determines ifa MsgID for the mail job is in the cache, and if yes, obtains a mappingfor the MsgID from the cache and processes the mail job, if the MsgIDfor the mail job is not in the cache, retrieves the MsgID from adatabase, caches the retrieved MsgID into the cache, obtains a mappingfor the retrieved MsgID from the cache and processes the mail job, andpurges without using weights and heuristics the cache of the MsgID's.20. A computer-readable medium according to claim 19, wherein the memorycomprises a disk memory.